[ATM] Big mirrors (was ATM Digest, Vol 7, Issue 23)

[Hugues.Laroche@ses-astra.com]

Hi Bill,

>Mr Volna is a member of our club, ( The Minnesota Astronomical Society ).
>He gave a wonderful talk to our club earlier this year about his mirror
and
>lens making escapades.  He has had this mirror blank for sale for number
of
>years but to date no one has demonstrated that they have adequate
equipment,
>tools energy and resources to make the mirror into a successful telescope.
>The issues of dealing with such a mirror are staggering.  How do you
grind,
>polish figure and test such a beast, how do you move it, where on earth
will
>you get it coated?
>Bill Kocken

Ah yes, I knew this link and had noticed that the ad had disappeared.
So this 72" is still for sale?

It is true that the issues grow very rapidly with the mirror size. I am
busy in solo with a
very big one (45") and can tell you that everything is huge and takes long.
Just rotating it on the polishing stand is a problem. Moving it to and back
from the
test stand is a problem. Having it aluminised will defintetly be a big
problem,
especially in Europe where aluminising costs a fortune. I think about
spray-silvering
at first. Having it truly clean is not so easy. However my biggest problems
are related
to the tools: difficult to garantee the structural stability and
cleanliness in storage.
So far I worked by hand, but am getting the material to make a machine,
since my
efforts to get the correction down from b=-2.9 to b=-1.0 look nearly w/o
effect.

Hugues



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